Technical Field
The disclosure relates to a control device for an internal combustion engine, which uses a water vapor parameter to control operation of the internal combustion engine, and the water vapor parameter represents the ratio or amount of water vapor in the air drawn into an intake passage.
Related Art
As a control device for an internal combustion engine, the applicant has previously proposed a control device as set forth in WO2016/017214 (Patent Document 1). The control device calculates the EGR (exhaust gas recirculation) ratio REGRT by the calculation processing shown in FIG. 4 of the document. In the case of the calculation processing, first, an ideal in-cylinder gas amount Gth is calculated by the calculation processing shown in FIG. 5 of the document, and a reference in-cylinder gas temperature Tcylstd is calculated by searching a map according to the engine speed NE or the like; next, an in-cylinder gas temperature Tcyl is calculated by the calculation processing shown in FIG. 6 of the document (step 1 to step 3). Then, an in-cylinder gas amount Gact is calculated by using formula (9), and finally the EGR ratio REGRT is calculated by using formula (12) (step 4 to step 5).
Further, in the ignition timing control processing shown in FIG. 7 of the document, an optimum ignition timing IGMBT is calculated according to the engine speed NE and the EGR ratio REGRT, and a final ignition timing IGLOG is calculated by using the optimum ignition timing IGMBT (step 31 to step 36). Then, a gas mixture is ignited using a spark plug at a timing corresponding to the ignition timing IGLOG.
Generally speaking, in an internal combustion engine, the air drawn from the atmosphere (hereinafter referred to as “intake air”) is used to generate the gas mixture, and the intake air may be in a high-humidity state in rainy weather. In this case, the water vapor in the intake air has the following characteristics: the water vapor can reduce the combustion temperature of the gas mixture like the recirculated gas does, and the water vapor has a higher capability than the recirculated gas in reducing the combustion temperature.
However, when the control device of Patent Document 1 calculates the EGR ratio, the humidity state of the intake air is not taken into consideration. Therefore, under a high-humidity environment condition, for example, the intake air in the high-humidity state may lead to an unduly low combustion temperature and an unstable combustion state, and thus surging or misfiring may occur. Further, for the same reason, the ignition timing may be controlled unduly toward the retarded side, resulting in poor fuel economy performance.